Getting a 9 seater (and converting from a 17 seater)

Hey folks,
I've been thinking to get a 9 seater for leisure use/road trips etc. Was thinking a classic Landrover but was then thinking, why not get a 17 seat jumbo transit, and remove 8 of the seats in the back to leave driver +2 up front, and 6 in the back so I'd have a LOT more space to take bikes and the likes and to have comfortable standing room etc and possibly down the line look at converting to some sort of 9 seat camper :pac:

I'd like to keep it to 9 seats so it can be driven on a regular B license. I also saw these folding jump seats and if I could get 2 x 3 seater ones, or 3 x 2 seater if they only come in max 2 seat, that would be great too:
https://www.youtube.com/watch?v=AqxHj12MHk4

I just have a few questions:

Is it simply a case of going to the VRT centre and declaring that what would be down as say a 17 seater on its log book, is now a 9 seater?

Would I need to go BACK again to get the jump seats ok'd if I get them after it's re-reg'd as a 9 seater, or I should be fine just to take out seats and replace with these myself?

Will it just be a regular DOE test, checking the usual they do with a van and checking all 9 belts work properly etc, or would there be more to it?

Any other things to highlight or any advice at all would be appreciated